8.6 A full-duplex line driver for Gigabit Ethernet with rail-to-rail class-AB output stage in 28nm CMOS

Gigabit Ethernet PHY (GPHY) transceivers find wide use in SoCs and standalone PHY chips with hundreds of millions of ports shipped every year. Transceiver design has recently focused on power reduction driven by the need for higher port density and throughput with minimum energy and thermal cost. The line drivers that deliver power from a high voltage supply to remote 100Ω differential loads dominate the GPHY power consumption. The supply voltage determined by the transmit amplitude specs (e.g., 2Vppdiff for 1000BASE-T/100BASE-TX Ethernet) does not scale with technology. This paper presents an architecture that enables rail-to-rail full-duplex operation for high voltage efficiency resulting in a 2.5V GPHY driver in 28nm CMOS that saves 24% power from the mainstream 3.3V drivers.